1. Field of the Invention
This invention relates generally to plug valves for controlling fluid flow and more particularly to trunnioned ball valves designed to operate under a wide range of temperature and pressure conditions, including conditions of high pressure, and utilizing sealing means incorporating elastomeric materials. The valves of this invention include axially movable sealing assemblies mounted in seat recesses formed within the inlet and outlet flow passages adjacent to the plug member. The valves disclosed herein may be used in oil and gas pipelines, and in refinery, chemical, nuclear, compressor and other industrial installations.
2. Description of the Prior Art
Gate and ball valves incorporating axially movable sealing assemblies with elastomeric sealing elements made of materials such as rubber, polytetrafluoroethylene ("TEFLON" -- Trade Mark of E. I. duPont de Nemours and Co.) or a fully saturated fluorocarbon copolymer of chlorotrifluoroethylene and vinylidene fluoride ("KEL-F" -- Trade Mark of M. W. Kellogg Company) are known in the prior art. See, for example, Canadian Patent No. 801,600, W. E. Lowrey, issued Dec. 17, 1968. It is known to design the sealing assemblies for such valves in such a way that, where the pressure within the conduit exceeds that within the valve chamber, the pressure on the side of the sealing assembly remote from the plug member substantially exceeds that on the side adjacent to the plug member whereby the sealing assembly is forced into tight sealing engagement with the plug. See, for example, U.S. Pat. No. 3,460,802, J. M. Colby et al, Aug. 12, 1969. Colby also discloses bevelling of the inlet and outlet flow passages behind the shoulder of the seat assembly so as to provide, when the valve is in the open position, a turbulent flow that scours out debris or particles which may have become lodged behind the shoulders when the valve was closed. Lowrey, supra, also discloses the use of a spring means to bias the seat assembly against the plug member when there is no flow and the pressure within the conduit does not exceed that within the valve chamber outside the line of sealing contact between the sealing member and the plug member. It is known, in such valves, to utilize a sealing assembly comprising a seat ring and a retainer ring interfitting to define an annular groove, with an annular elastomeric sealing member held within that groove under pressure and brought to bear against the plug member in sealing engagement. See Lowrey, supra, and also Canadian Patent No. 825,032, E. R. Atkinson et al, Oct. 14, 1969. It is further known in such valves to provide means for introducing lubricant sealant to the area of sealing contact between the sealing member and the plug member; see, for example, Canadian Patent No. 830,323, M. T. Works, Dec. 23, 1969. Finally, it is known, in trunnioned ball valves, to provide stop means at the lowermost end of the lower trunnion for limiting the rotation of the plug member to a range of 90.degree. between the open and closed positions in order to facilitate the precise positioning of the plug member in the conditions of zero flow and maximum flow. See, for example, Canadian Patent Nos. 911,973 and 921,451, A. D. Oliver, Oct. 10, 1972 and Feb. 20, 1973 respectively. By positioning a stop device in the lower trunnion, it is possible to avoid misalignment caused by stresses encountered during use of the valve, and it is possible to provide precise initial alignment in spite of "tolerance stackup" due to manufacturing tolerances in the various parts of the valve.